Electric motors are used in a range of aerospace applications, for example to drive hatches or doors between their open and closed positions or to drive flaps or the like. In some applications, where rapid movement is to be achieved, the motor must be able to rotate at very high speeds. It is important, in such applications, to provide a brake assembly to permit rapid deceleration of the motor to avoid damage to the aircraft when the hatch, door, flap or other component approaches the end of its range of movement, or to stop the component in a desired location. Additionally, the brake assembly may be required to operate as a primary or secondary holding means to prevent movement of, for example, the hatch or door away from a predetermined position.
In a typical brake assembly, for example as described in U.S. Pat. No. 4,921,078, a plurality of brake discs are provided, alternate ones of the brake discs being rotatable with the output of the motor, the remaining discs being non-rotatable. An electromagnetic actuator is provided to control the compressive load applied to the discs, thereby controlling the magnitude of a braking force applied to the motor. The discs are typically formed from steel, phosphor bronze or a combination of both and typically have a friction coefficient falling within the range 0.1 to 0.2. Brake assemblies of this type operate whilst immersed in oil to avoid excessive wear or for cooling purposes.
For a number of applications, such a brake assembly provides an adequate braking force. However, in aerospace applications, where component weight and size are of great importance, the number and size of traditional brake discs required may result in an undesirably large and heavy assembly. Also, in some high load applications, for example, it is desirable to be able to apply a greater braking force, for example to stop a motor operating at speeds of the order of 15,000 rpm within a fraction of a second. It is further desirable to provide a brake assembly which is readily serviceable and which requires little setting or adjustment upon assembly, and which may be operated satisfactorily without being immersed in oil.